Flaying Tendrils

Oracle Text

Devoid (This card has no color.)

All creatures get -2/-2 until end of turn. If a creature would die this turn, exile it instead.

Card Rulings

1/22/2016 Only creatures that are on the battlefield as Flaying Tendrils resolves will get -2/-2. However, any creature that would die that turn will be exiled, even if it wasn’t on the battlefield or wasn’t a creature as Flaying Tendrils resolved.
1/22/2016 Creatures that Flaying Tendrils would cause to die will be exiled instead. The game doesn’t check to see which creatures die until after Flaying Tendrils has finished resolving.